PRINCE WILLIAM COUNTY, Va. (WUSA9) -- On a beautiful Saturday afternoon, runners fought an uphill battle in the Marine Corp 17.75k run.

"1775 is when the Marine Corp was created we are here to celebrate and go on to the Marine Corps Marathon," Jonathan White, Gunnery Sgt. said.

But for Marine Corporal Aaron Thomas he was not only thinking about the miles ahead but about this week's tragedy at the Marine base in Quantico.

"When I heard about it my heart sank. The military brotherhood is strong and it doesn't matter which branch but it hurts even more when it's your own branch, the Marine Corps," he said.

In the Taylor Hall Barracks, It was discovered that 25-year-old Sgt. Eusebio Lopez gunned down 19-year-old Lance Cpl. Lance Sara Castromata and 23-year-old Cpl. Jacob Wooley. All three were staff members of the Officer Candidate School.

Less than 48 hours after three lives were lost on base, fellow marines came together to run but many with heavy hearts.

"It made me pray a little harder to run not just for myself but for them," Thomas said.

Sgt. Roy Blakeburn, retired US Marine said, "Something like that happens everyone suffers we all suffer for that."

Authorities have not spelled out a motive for the bloodshed but say it was an isolated incident and have not ruled out a domestic situation could have been a contributing factor.

"The help is there you don't have to go it alone. I never understood why you take your own life but I've never been that low. You don't have to go it alone go get help," Blakeburn said.

The shooting at Quantico is the second tragedy to hit the Marine Corps in less than a week, seven Marines were killed in an explosion during a training exercise in Nevada.